A dicentric chromosome is an abnormal chromosome with two centromeres. It is formed through the fusion of two chromosome segments, each with a centromere, resulting in the loss of acentric fragments (lacking a centromere) and the formation of dicentric fragments. The formation of dicentric chromosomes has been attributed to genetic processes, such as Robertsonian translocation and paracentric inversion. Dicentric chromosomes have important roles in the mitotic stability of chromosomes and the formation of pseudodicentric chromosomes. Their existence has been linked to certain natural phenomena such as irradiation and have been documented to underlie certain clinical syndromes, notably Kabuki syndrome. The formation of dicentric chromosomes and their implications on centromere function are studied in certain clinical cytogenetics laboratories. Formation Most dicentric chromosomes are known to form through chromosomal inversions, which are rotations in regions of a chromosome due to chromosomal breakages or intra-chromosomal recombinations. Inversions that exclude the centromere are known as paracentric inversions, which result in unbalanced gametes after meiosis. During prophase of meiosis I, homologous chromosomes form an inversion loop and crossover occurs. If a paracentric inversion has occurred, one of the products will be acentric, while the other product will be dicentric. The dicentric chromatid is pulled apart during anaphase of meiosis I with such force that the chromosome breaks at random positions. These broken fragments result in deletions of genes that lead to genetically unbalanced gametes. This can have severe consequences, contributing to the development of genetic disorders such as Kabuki syndrome and Edwards syndrome. Irradiation Radiation is known to induce abnormalities in the nuclei of cells. Dicentric chromosomes were first detected in lymphocytes from blood smears of civil and military personnel who were assigned to deal with the aftermath of the 1986 Chernobyl nuclear disaster (liquidators). Radiation increases the probability that dicentric chromosomes form after every mitotic event, creating physical bridges between them in anaphase and telophase. As these chromosomes are pulled apart, the chromosome bridges break, resulting in the formation of "tailed" nuclei, protrusions of the nuclei into the cytoplasm. Telomeres When telomeres of chromosomes shorten with continued cell divisions, the chromosome ends may also fuse, forming dicentric chromosomes. This is considered "crisis", a type of cell cycle arrest, and most cells in this state suffer apoptosis. The resulting dicentric chromosomes are highly unstable, giving rise to chromosomal translocations, deletions and amplifications, such as the Robertsonian translocation. This results in broken, deleted gene products of